1. Field of the Invention
The present invention relates to a method for the preparation of fiber stock, for the production of paper or cardboard.
2. Description of the Related Art
Fiber stock, for the production of paper and carton cardboard, is processed in the stock preparation that is located prior to the paper machine so that the desired attributes, such as, for example, mechanical characteristics, optical characteristics, etc., are achieved. Especially the mechanical characteristics including consistency characteristics are influenced by the so-called freeness of the fiber stock suspension. This freeness is an indicator as to how easily the fiber stock suspension can be dewatered. A certain level of freeness can be achieved by more or less intensive refining of the fibers in so-called refiners. This involves the fibers being shortened, fibrillated and crushed. This process renders the fibers flexible and increases their specific surface, so that the number of possible bonding points between the fibers is increased during sheet formation. This leads to an increase of the mechanical strength of the paper or carton produced from these fibers. The required refining process uses a considerable amount of energy. Approximately 120 kWhr to 200 kWhr are required per ton of fiber material, depending upon the type of pulp or fiber, the freeness as well as other refining parameters. The conventional method is to refine the fiber stock before, or after, the direct addition of the usual fillers, for example, calcium carbonate, titanium dioxide, etc. The aforementioned high energy volumes are utilized for this.
Loading with a precipitation product, for example a filler, may occur, for example, through a so-called Fiber Loading™ process, as described in U.S. Pat. No. 5,223,090. In this type of “Fiber Loading™” process, an additive, especially a filler, is deposited onto the moistened fiber surfaces of the fibrous material. The fibers may be loaded with calcium carbonate. Moreover, calcium oxide and/or calcium hydroxide are added to the moist, disintegrated fibrous material so that at least a part of this associates itself with the water that is contained in the fibrous material. The so treated fibrous material is subsequently treated with carbon dioxide. In the method that is known from U.S. Pat. No. 5,223,090, the “Fiber Loading™” process can occur inside a refiner.
It is thus a known procedure to subject the stock or pulp to a loading process with which calcium carbonate is produced. However, it remains an open question as to how this treated stock is to be treated optimally, in other words to be refined, with regard to its mechanical, chemical and physical characteristics. What is needed in the art is a more economic and efficient refining process.